A typical television production facility includes at least one video switcher having the capability of switching video input signals from one or more sources, such as cameras, video tape recorders, servers, digital picture manipulators (video effects devices), character generators, and the like, to one or more outputs. Many present day video switchers, such as the Kalypso family of video production switchers manufactured by Thomson Grass Valley Group, have the ability to manipulate one or more input signals to create an effect. Common video effects include fades and wipes, whereas more sophisticated effects include: page turns, page rolls, splits, mirrors, ripples and spheres, as well as size and position modulation. In practice, an operator will first create one or more desired effects for storage to enable subsequent recall. Upon recall, the video effect can undergo mixing with one or more other effects prior to execution.
A video effect comprises at least one, and often a succession of keyframes. Each keyframe corresponds to a storage register that contains data that defines a single set of control settings associated with that effect. The keyframe(s) define all or at least part of the operating state of the switcher. The settings associated with each keyframe undergo storage in an associated memory or register. A typical video switcher has finite number of register locations for storing keyframe settings.
The production and mixing of video effects that undergo live transmission requires a high degree of control to avoid any visible artifacts, such as unexpected pops, flashes, or abrupt changes. Thus, a problem exists in safely transitioning from one effect to another. Generally, operators avoid changing from one effect to another while the video for the contributing channels currently undergoes live transmission. If the state of the first keyframe of the newly recalled effect differs in any way to the current state of the switcher, the output can suddenly “pop” to the new state.
The problem of recalling an effect while enabled channels are on air has been partially addressed by a technique known as effects dissolve. Some present day video switchers afford operators the ability to interpolate from any switcher state to the state of the first keyframe of an effect. However, with the effects dissolve technique, all elements of the video effect undergo interpolation, not just those that undergo change during the video effect. In this way, the current state of the switcher transitions incrementally towards the absolute state of the first keyframe. Thus, effects dissolve does not act like a special function. Also, the effects dissolve takes place prior to the execution of the video effect and thus constitutes an additive behavior to the original effect. Upon reaching the first keyframe, the video effect executes in the traditional way. Moreover, effects dissolve does not support interpolation based upon keyframes, is not reversible, and provides no path controls.
Thus a need exists for technique for recalling a stored effect in a manner that avoids such visual artifacts and overcomes other disadvantages of the prior art.